In most fuel injection systems, fuel is sprayed into a combustion space through one or more relatively tiny nozzle orifices at a relatively high pressure. A needle check valve normally blocks the nozzle orifices, but is capable of moving to an open position when fuel pressure is above a valve opening pressure sufficient to overcome a bias that is acting on the needle valve. In a typical injection sequence, the needle valve member moves to an open position, an amount of fuel is injected into the engine cylinder, and the needle valve then closes to end the injection event. In order to increase combustion efficiency, and hence lower the presence of unburned hydrocarbons and NOx in the emissions, engineers are continuously seeking ways to improve the mixing of the fuel with air when the same is sprayed into the engine cylinder. The conventional wisdom has long been that the best mixing of fuel and air occurs when the fuel is atomized. The conventional wisdom with regard to improving atomization has generally been to make the nozzle orifices as small as possible and the fuel pressure as high as possible. However, because of material and machining constraints, nozzle orifices can realistically be made only so small and the fuel can only be pressurized so high.
The present invention is directed to improving combustion efficiency, and hence lowering undesirable emissions, by injecting fuel in a manner different from that of the prior art.